Embolic protection is a concept of growing clinical importance directed at reducing the risk of embolic complications associated with interventional (i.e., transcatheter) and surgical procedures. In therapeutic vascular procedures, liberation of embolic debris (e.g., thrombus, clot, atheromatous plaque, etc.) can obstruct perfusion of the downstream vasculature, resulting in cellular ischemia and/or death. The therapeutic vascular procedures most commonly associated with adverse embolic complications include: carotid angioplasty with or without adjunctive stent placement; and revascularization of degenerated saphenous vein grafts. Additionally, percutaneous transluminal coronary angioplasty (PTCA) with or without adjunctive stent placement, surgical coronary artery by-pass grafting, percutaneous renal artery revascularization, and endovascular aortic aneurysm repair have also been associated with complications attributable to atheromatous embolization. The use of embolic protection devices to capture and remove embolic debris, consequently, may improve patient outcomes by reducing the incidence of embolic complications.
Embolic protection devices typically act as an intervening barrier between the source of the clot or plaque and the downstream vasculature. Numerous devices and methods of embolic protection have been used adjunctively with percutaneous interventional procedures. These techniques, although varied, have a number of desirable features including: intraluminal delivery; flexibility; trackability; small delivery profile to allow crossing of stenotic lesions; dimensional compatibility with conventional interventional implements; ability to minimize flow perturbations; thromboresistance; conformability of the barrier to the entire luminal cross section (even if irregular); and a means of safely removing the embolic protection device and trapped particulates. There are two general strategies for achieving embolic protection: techniques that employ occlusion balloons; and techniques that employ an embolic filter. The use of embolic filters is a desirable means of achieving embolic protection because they allow continuous perfusion of the vasculature downstream to the device.
Occlusion balloon techniques have been taught by the prior art and involve devices in which blood flow to the vasculature distal to the lesion is blocked by the inflation of an occlusive balloon positioned downstream to the site of intervention. Following therapy, the intraluminal compartment between the lesion site and the occlusion balloon is aspirated to evacuate any thrombus or atheromatous debris that may have been liberated during the interventional procedure. The principle drawback of occlusion balloon techniques stems from the fact that during actuation, distal blood flow is completely inhibited, which can result in ischemic pain, distal stasis/thrombosis, and difficulties with fluoroscopic visualization due to contrast wash-out through the treated vascular segment.
A prior system described in U.S. Pat. No. 4,723,549 to Wholey, et al. combines a therapeutic catheter (e.g., angioplasty balloon) and integral distal embolic filter. By incorporating a porous filter or embolus barrier at the distal end of a catheter, such as an angioplasty balloon catheter, particulates dislodged during an interventional procedure can be trapped and removed by same therapeutic device responsible for the embolization. One known device includes a collapsible filter device positioned distal to a dilating balloon on the end of the balloon catheter. The filter comprises a plurality of resilient ribs secured to circumference of the catheter that extend axially toward the dilating balloon. Filter material is secured to and between the ribs. The filter deploys as a filter balloon is inflated to form a cup-shaped trap. The filter, however, does not necessarily seal around the interior vessel wall. Thus, particles can pass between the filter and the vessel wall. The device also lacks longitudinal compliance. Thus, inadvertent movement of the catheter results in longitudinal translation of the filter, which can cause damage to the vessel wall and liberate embolic debris.
Other prior systems combine a guide wire and an embolic filter. The embolic filters are incorporated directly into the distal end of a guide wire system for intravascular blood filtration. Given the current trends in both surgical and interventional practice, these devices are potentially the most versatile in their potential applications. These systems are typified by a filter frame that is attached to a guide wire that mechanically supports a porous filter element. The filter frame may include radially oriented struts, one or more circular hoops, or a pre-shaped basket configuration that deploys in the vessel. The filter element is typically comprised of a polymeric or metallic mesh net, which is attached to the filter frame and/or guide wire. In operation, blood flowing through the vessel is forced through the mesh filter element thereby capturing embolic material in the filter.
Early devices of this type are described in the art, for example in U.S. Pat. No. 5,695,519 to Summers, et al., and include a removable intravascular filter mounted on a hollow guide wire for entrapping and retaining emboli. The filter is deployable by manipulation of an actuating wire that extends from the filter into and through the hollow tube and out the proximal end. During positioning within a vessel, the filter material is not fully constrained so that, as the device is positioned through and past a clot, the filter material can potentially snag clot material creating freely floating emboli prior to deployment. The device also lacks longitudinal compliance.
Another example of a prior device, taught in U.S. Pat. No. 5,814,064 to Daniel, et al., uses an emboli capture device mounted on the distal end of a guide wire. The filter material is coupled to a distal portion of the guide wire and is expanded across the lumen of a vessel by a fluid activated expandable member in communication with a lumen running the length of the guide wire. During positioning, as the device is passed through and beyond the clot, filter material may interact with the clot to produce emboli. The device also lacks longitudinal compliance.
Another device, taught in U.S. Pat. No. 6,152,946 to Broome, et al., which is adapted for deployment in a body vessel for collecting floating debris and emboli in a filter, includes a collapsible proximally tapered frame to support the filter between a collapsed insertion profile and an expanded deployment profile. The tapered collapsible frame includes a mouth that is sized to extend to the walls of the body vessel in the expanded deployed profile and substantially longitudinal struts that attach and tether the filter frame to the support wire. This device also lacks substantial longitudinal compliance. This device has the additional drawback of having an extended length due to the longitudinally oriented strut configuration of the tapered frame. This extended length complicates the navigation and placement of the filter within tortuous anatomy.
A further example of an embolic filter system, found in PCT WO 98/33443, involves a filter material fixed to cables or spines of a central guide wire. A movable core or fibers inside the guide wire can be utilized to transition the cables or spines from approximately parallel to the guide wire to approximately perpendicular the guide wire. The filter, however, may not seal around the interior vessel wall. Thus, particles can pass between the filter and the entire vessel wall. This umbrella-type device is shallow when deployed so that, as it is being closed for removal, particles have the potential to escape.
In summary, disadvantages associated with predicate devices include lack of longitudinal compliance, extended deployed length of the frame and associated tethering elements, and inadequate apposition and sealing against a vessel wall. Without longitudinal compliance, inadvertent movement of the filter catheter or support wire can displace the deployed filter and damage a vessel wall and/or introgenic vascular trauma, or, in extreme cases, result in the liberation of embolic debris. An extended deployed length aggravates proper filter deployment adjacent to vascular side branches or within tightly curved vessels. Inadequate filter apposition and sealing against a vessel wall has the undesirable effect of allowing emboli passage.
To ensure filter apposition and sealing against a vessel wall, without inducing undue vascular trauma, the radial force exerted by the filter against the vessel wall should be optimized. Typical methods used to increase the radial force exerted by the filter include, for example, increasing the cross-sectional area (moment of inertia and therefore the stiffness) of the filter support frame and in particular the tethering elements of the frame. Enhanced radial force can also be achieved by incorporating additional support members or by enlarging the “relaxed” or deployed diameter of the filter frame relative to the diameter of the vessel into which it is deployed. These methods typically have the undesirable side effects of degrading the longitudinal compliance, adding to the compressed delivery profile, and, in some cases, increasing the deployed length. Some methods used to increase the radial force (for example, stiffer support frames) have the additional drawback of requiring thicker-walled, larger profile, delivery catheters. To accommodate the increased pressure exerted by the stiff frame (constrained within the delivery catheter) a commensurately thicker catheter wall is required, compromising the delivery profile.